Embodiments of the invention are generally related to the field of electronic amplifiers and electronic devices using the amplifiers, and more particularly, to a Class-E amplifier and a lighting ballast using the Class-E amplifier.
Class-E amplifiers are highly efficient switching power amplifiers, operating at high frequencies. Referring to FIG. 1, a typical class-E amplifier 10 includes a transistor 12, such as a metal-oxide-silicon field-effect transistor (MOSFET), connected via a serial-LC-circuit 14 to a load 16, and connected via a large inductor 18 to a power source 20. Capacitor 22 represents parasitic capacitance of the transistor 12 or may include an additional capacitor. At an ON stage of the MOSFET, the voltage across the MOSFET is close to zero, and when the MOSFET is OFF, the current through the MOSFET is close to zero. Together with capacitor 22, the serial-LC-circuit 14 shapes the voltage and current waveforms to prevent simultaneous high voltage and high current in the transistor 12, that minimizes power dissipation, especially during the switching transitions. Accordingly a significant advantage of Class-E amplifiers is lower power dissipation resulting in higher efficiency. On the other hand, the class E amplifier generates substantial harmonic energy while inducing a high peak voltage for the MOSFET drain, which causes a risk of damage to the MOSFET.
It is desirable to have an improved Class-E amplifier with harmonic reduction design.